Apparatus for performing a self-test of kidney dialysis membrane

• US 5,486,286 A
• Filed: 09/14/1993
• Issued: 01/23/1996
• Est. Priority Date: 04/19/1991
• Status: Expired due to Term

• Current Assignee: Baxter International Inc.
• Original Assignee: Althin Medical, Inc.
• Inventors: Long, Jean M., Hogard, Michael E., Kelly, Thomas D., Elsen, Raymond, Smejtek, Dalibor J., Connell, Mark E., Johnson, Harley D., Preston, William G. Jr., Bedient, Robert A., Peterson, Bruce A.
• Primary Examiner(s): Drodge, Joseph W.
• Application Number:
  US08/122,047
• Time in Patent Office: 861 Days
• Field of Search: 210/85, 210/87-90, 210/93, 210/137, 210/141, 210/195.2, 210/257.2, 210/258, 210/321.65, 210/321.71, 210/646, 210/647, 210/929, 604/425, 604/6
• US Class Current: 210/87
• CPC Class Codes: A61M 1/16 with membranes
• CPC Class Codes: A61M 1/1607 before use, i.e. upstream of dialyser
• CPC Class Codes: A61M 1/1613 Profiling or modelling of patient or predicted treatment evolution or outcome
• CPC Class Codes: A61M 1/165 with a dialyser bypass on the dialysis fluid line
• CPC Class Codes: A61M 1/1656 Apparatus for preparing dialysates
• CPC Class Codes: A61M 1/1664 with temperature control
• CPC Class Codes: A61M 1/1666 by dissolving solids
• CPC Class Codes: A61M 1/168 Sterilisation or cleaning before or after use
• CPC Class Codes: A61M 1/1684 Checking the module characteristics before reuse
• CPC Class Codes: A61M 1/1686 by heat
• CPC Class Codes: A61M 1/1688 with recirculation of the sterilising fluid
• CPC Class Codes: A61M 1/169 using chemical substances
• CPC Class Codes: A61M 1/1692 Detection of blood traces in dialysate
• CPC Class Codes: A61M 1/1694 with recirculating dialysing liquid
• CPC Class Codes: A61M 1/341 by measuring the filtrate rate or volume
• CPC Class Codes: A61M 1/3626 Gas bubble detectors
• CPC Class Codes: A61M 2039/1005 Detection of disconnection
• CPC Class Codes: A61M 2205/3313 used specific wavelengths
• CPC Class Codes: A61M 2205/3317 Electromagnetic, inductive or dielectric measuring means
• CPC Class Codes: A61M 2205/3324 PH measuring means
• CPC Class Codes: A61M 2205/3334 : Measuring or controlling the flow rate
• CPC Class Codes: A61M 2205/3368 : Temperature
• CPC Class Codes: A61M 2205/505 : Touch-screens; Virtual keyboard or keypads; Virtual buttons; Soft keys; Mouse touches
• CPC Class Codes: A61M 2205/52 : with memories providing a history of measured variating parameters of apparatus or patient
• CPC Class Codes: G06F 3/0482 : Interaction with lists of selectable items, e.g. menus
• CPC Class Codes: G06F 3/04847 : Interaction techniques to control parameter settings, e.g. interaction with sliders or dials
• CPC Class Codes: G16H 20/40 : relating to mechanical, radiation or invasive therapies, e.g. surgery, laser therapy, dialysis or acupuncture
• CPC Class Codes: G16H 40/63 : for local operation
• CPC Class Codes: Y10S 210/929 : Hemoultrafiltrate volume measurement or control processes

Abstract

A number of improvements relating to methods and apparatuses for kidney dialysis are disclosed. These include checking of dialysate bypass status using flow measurement; using a flow sensor to confirm the absence of ultrafiltration during bypass; automatic testing of ultrafiltration function by removal of a discrete volume from a portion of the dialysate flow path coupled with a pressure test of that part of the flow path; using a touch screen user interface; bar graph profile programming of ultrafiltration, sodium, and bicarbonate parameters; using a RAM card to upload treatment instructions to, and to download treatment data from, the machine; automatic setting of proportioning mode (acetate or bicarbonate) based on connections of concentrate lines; predicting dialysate conductivity values based on brand and formulation of concentrates; minimizing no-flow dead time between dialysate pulses; initiating operation in a timed mode from a machine power-off condition; preserving machine mode during machine power-fail condition; calibration scheduling and reminding; automatic level adjusting; and blood leak flow rate detecting.

Claims

1. A kidney dialysis machine comprising:

(a) a dialyzer having a dialysate compartment, a blood compartment separated from the dialysate compartment by a dialysis membrane, a dialysate input, a dialysate output, a blood input, and a blood output;

(b) means for preparing dialysate and means for circulating the dialysate through a dialysate circuit, the dialysate circuit including the dialysate compartment, the dialysate input and the dialysate output of the dialyzer;

(c) means for effecting extracorporeal circulation of blood from a dialysis patient through a blood circuit, the blood circuit including the blood compartment, the blood input, and the blood output of the dialyzer;

(d) means for delivering a first volume of dialysate to the dialysate compartment of the dialyzer;

(e) means for removing, simultaneously with delivering the first volume, a second volume of dialysate, equal to the first volume, from the dialysate compartment of the dialyzer;

(f) means for creating a volumetrically closed hydraulic loop in the dialysate circuit between said means for delivering the first volume and said means for removing the second volume;

(g) pressure-monitoring means for monitoring hydraulic pressure in the closed loop against pressure alarm limits;

(h) means for effecting a preselected net passage of liquid from the blood compartment through the dialysis membrane to the dialysate compartment, said means comprising ultrafiltrate removal means situated in the closed loop, said ultrafiltrate removal means being operable to remove a preselected volume of liquid from the closed loop; and

(i) self-test means operative to perform, upon actuation, an automatic test of said means for effecting a preselected net passage of liquid from the blood compartment through the dialysis membrane to the dialysate compartment, wherein, during the test, said ultrafiltrate removal means removes a preset volume of liquid from the closed loop and said pressure monitoring means monitors a corresponding drop in pressure in the closed loop for a preset amount of time.

2. A kidney dialysis machine as recited in claim 1 wherein said ultrafiltrate removal means comprises an ultrafiltration flow meter situated in the dialysate circuit between said means for delivering the first volume and said means for delivering the second volume, the ultrafiltration flow meter operable to remove a preselected volume of liquid from the dialysate circuit between said means for delivering the first volume of dialysate and said means for delivering the second volume of dialysate.

3. A kidney dialysis machine as recited in claim 1 wherein said means for delivering a first volume of dialysate to the dialysate compartment of the dialyzer and said means for simultaneously removing a second volume of dialysate equal to the first volume from the dialysate compartment of the dialyzer collectively comprise a flow equalizer comprising a first chamber and a second chamber substantially equal in volume to the first chamber, each chamber being divided by a flexible membrane impervious to dialysate into a pre-dialyzer compartment and a post-dialyzer compartment, the pre-dialyzer compartment of the first chamber and the post-dialyzer compartment of the second chamber being operable to alternately fill and empty simultaneously, and the post-dialyzer compartment of the first chamber and the pre-dialyzer compartment of the second chamber being operable to alternately fill and empty simultaneously alternately with the pre-dialyzer compartment of the first chamber and the post-dialyzer compartment of the second chamber.

4. A kidney dialysis machine as recited in claim 1 wherein said self-test means further comprises means for verifying that the drop in pressure remains within pressure alarm limits for a preset amount of time.

5. A kidney dialysis machine comprising:

(a) a dialyzer with a dialysate compartment, a blood compartment separated from the dialysate compartment by a dialysis membrane, a dialysate input, a dialysate output, a blood input, and a blood output;

(b) means for preparing dialysate and means for circulating the dialysate through a dialysate circuit, the dialysate circuit including the dialysate compartment, the dialysate input and the dialysate output of the dialyzer;

c) means for effecting extracorporeal circulation of blood from a dialysis patient through a blood circuit, the blood circuit including the blood compartment, the blood input, and the blood output of the dialyzer;

(d) flow-equalizing means for delivering a first volume of dialysate to the dialysate compartment of the dialyzer and for removing, simultaneously with delivering the first volume, a second volume of dialysate, equal to the first volume, from the dialysate compartment of the dialyzer, said flow-equalizing means comprising a first chamber and a second chamber substantially equal in volume to the first chamber, each chamber being divided into a pre-dialyzer compartment and a post-dialyzer compartment, the pre-dialyzer compartment of the first chamber and the post-dialyzer compartment of the second chamber being operable to alternately fill and empty simultaneously, and the post-dialyzer compartment of the first chamber and the pre-dialyzer compartment of the second chamber being operable to alternately fill and empty simultaneously alternately with the pre-dialyzer compartment of the first chamber and the post-dialyzer compartment of the second chamber; and

(e) each pre-dialyzer compartment having an inlet and an outlet and each post-dialyzer compartment has an inlet and an outlet, said flow-equalizing means further comprising inlet valves each having an outlet hydraulically coupled to the inlet of the corresponding pre-dialyzer and post-dialyzer compartment, and outlet valves each having an inlet hydraulically coupled to the outlet of a corresponding pre-dialyzer and post-dialyzer compartment, wherein the inlets of the valves coupled to the inlets of the pre-dialyzer compartments are hydraulically coupled together and the inlets of the valves coupled to the inlets of the post-dialyzer compartments are hydraulically coupled together so as to form a flow-equalizer inlet, and wherein the outlets of the valves coupled to the outlets of the pre-dialyzer compartments are hydraulically coupled together and the outlets of the valves coupled to the outlets of the post-dialyzer compartments are hydraulically coupled together so as to form a flow-equalizer outlet.

6. A kidney dialysis machine as recited in claim 5 further comprising sensing means for determining end-of-stroke times for the first and second chambers of the flow-equalizing means, said sensing means being hydraulically coupled to an outlet of the flow-equalizing means.

7. A kidney dialysis machine as recited in claim 6 wherein said sensing means comprises a first flow sensor hydraulically coupled to the outlets of the valves coupled to the outlets of the pre-dialyzer compartments, and a second flow sensor hydraulically coupled to the outlets of the valves coupled to the outlets of the post-dialyzer compartments.

8. A kidney dialysis machine as recited in claim 7 wherein the first and second flow sensors generate a shift signal whenever the corresponding pre- and post-dialyzer compartments have reached end-of-stroke the shift signal causing the inlet and outlet valves to shift whenever the pre- and post-dialyzer compartments have reached end of stroke.

9. A kidney dialysis machine comprising:

(a) a dialyzer having a dialysate compartment, a blood compartment separated from the dialysate compartment by a dialysis membrane, a dialysate input, a dialysate output, a blood input, and a blood output;

(b) means for preparing dialysate and means for circulating the dialysate through a dialysate circuit, the dialysate circuit including the dialysate compartment, the dialysate input and the dialysate output of the dialyzer;

(c) means for effecting extracorporeal circulation of blood from a dialysis patient through a blood circuit, the blood circuit including the blood compartment, the blood input, and the blood output of the dialyzer;

(d) flow-equalizing means for delivering a first volume of dialysate to the dialysate compartment of the dialyzer and for removing, simultaneously with delivering the first volume, a second volume of dialysate equal to the first volume from the dialysate compartment of the dialyzer, said flow-equalizing means comprising a first chamber and a second chamber substantially equal in volume to the first chamber, each chamber being divided into a pre-dialyzer compartment and a post-dialyzer compartment, and each pre-dialyzer compartment having an inlet and an outlet and each post-dialyzer compartment having an inlet and an outlet, the pre-dialyzer compartment of the first chamber and the post-dialyzer compartment of the second chamber being operable to alternately fill and empty simultaneously, and the post-dialyzer compartment of the first chamber and the pre-dialyzer compartment of the second chamber being operable to alternately fill and empty simultaneously alternately with the pre-dialyzer compartment of the first chamber and the post-dialyzer compartment of the second chamber; and

(e) first pressure equalizing means coupled to an inlet of the flow equalizing means for equilibrating hydraulic pressures at the inlets of the pre-dialyzer and post-dialyzer compartments and second pressure-equalizing means coupled to an outlet of the flow equalizing means for equilibrating hydraulic pressures at the outlets of the pre-dialyzer and post-dialyzer compartments.

10. A kidney dialysis machine comprising:

(a) a dialyzer with a dialysate compartment, a blood compartment separated from the dialysate compartment by a dialysis membrane, a dialysate input, a dialysate output, a blood input, and a blood output;

(b) means for preparing dialysate and means for circulating the dialysate through a dialysate circuit, the dialysate circuit including the dialysate at a dialysate flow rate compartment, the dialysate input and the dialysate output of the dialyzer;

(c) means for effecting extracorporeal circulation of blood from a dialysis patient through a blood circuit, the blood circuit including the blood compartment, the blood input, and the blood output of the dialyzer;

(d) means for delivering a first volume of dialysate to the dialysate compartment of the dialyzer;

(e) means for removing, simultaneously with delivering the first volume, a second volume of dialysate, equal to the first volume, from the dialysate compartment of the dialyzer, wherein said means for delivering a first volume and said means for removing a second volume collectively comprise a flow equalizer comprising a first chamber, a second chamber substantially equal in volume to the first chamber, an inlet, and an outlet, each chamber being divided into a pre-dialyzer compartment and a post-dialyzer compartment, the pre-dialyzer compartment of the first chamber and the post-dialyzer compartment of the second chamber being operable to alternately fill and empty simultaneously, and the post-dialyzer compartment of the first chamber and the pre-dialyzer compartment of the second chamber being operable to alternately fill and empty simultaneously alternately with the pre-dialyzer compartment of the first chamber and the post-dialyzer compartment of the second chamber;

(f) sensing means for determining end-of-stroke times for the first and second chambers of the flow-equalizer, said sensing means being hydraulically coupled to the flow-equalizer outlet; and

(g) means, responsive to said sensing means, operable to increase the dialysate flow rate if said sensing means detects an excessive end-of-stroke time.

11. A kidney dialysis machine comprising:

(a) a dialyzer with a dialysate compartment, a blood compartment separated from the dialysate compartment by a dialysis membrane, a dialysate input, a dialysate output, a blood input, and a blood output;

(b) means for preparing dialysate and means for circulating the dialysate through a dialysate circuit, the dialysate circuit including the dialysate compartment, the dialysate input and the dialysate output of the dialyzer;

(c) means for effecting extracorporeal circulation of blood from a dialysis patient through a blood circuit, the blood circuit including the blood compartment, the blood input, and the blood output of the dialyzer;

(d) means for delivering a first volume of dialysate to the dialysate compartment of the dialyzer;

(e) means for removing, simultaneously with delivering the first volume, a second volume of dialysate, equal to the first volume, from the dialysate compartment of the dialyzer, wherein said means for delivering a first volume and said means for removing a second volume collectively comprise a flow equalizer, comprising a first chamber and a second chamber substantially equal in volume to the first chamber, each chamber being divided into a pre-dialyzer compartment and a post-dialyzer compartment, the pre-dialyzer compartment of the first chamber and the post-dialyzer compartment of the second chamber being operable to alternately fill and empty simultaneously, and the post-dialyzer compartment of the first chamber and the pre-dialyzer compartment of the second chamber being operable to alternately fill and empty simultaneously alternately with the pre-dialyzer compartment of the first ,chamber and the post-dialyzer compartment of the second chamber, each pre-dialyzer compartment having an inlet and an outlet and each post-dialyzer compartment having an inlet and an outlet, the flow equalizer further comprising inlet valves each having an outlet hydraulically coupled to the inlet of the corresponding pre-dialyzer and post-dialyzer compartment, and outlet valves each having an inlet hydraulically coupled to the outlet of a corresponding pre-dialyzer and post-dialyzer compartment, wherein the inlets of the valves coupled to the inlets of the pre-dialyzer compartments are hydraulically coupled together and the inlets of the valves coupled to the inlets of the post-dialyzer compartments are hydraulically coupled together so as to form a flow-equalizer inlet, and wherein the outlets of the valves coupled to the outlets of the pre-dialyzer compartments are hydraulically coupled together and the outlets of the valves coupled to the outlets of the post-dialyzer compartments are hydraulically coupled together so as to form a flow-equalizer outlet; and

(f) first pressure equalizing means coupled to the inlet of the flow equalizer for equilibrating hydraulic pressures at the inlets of the pre-dialyzer and post-dialyzer compartments and second pressure-equalizing means coupled to the outlet of the flow equalizer for equilibrating hydraulic pressures at the outlets of the pre-dialyzer and post-dialyzer compartments.

12. A kidney dialysis machine, comprising:

(a) a dialyzer having a dialysate compartment, a blood compartment separated from the dialysate compartment by a dialysis membrane, a dialysate input, a dialysate output, a blood input, and a blood output;

(b) a source of liquid dialysate;

(c) a dialysate supply pump for circulating the dialysate from the dialysate source through a dialysate circuit, the dialysate circuit including the dialysate compartment, the dialysate input, and the dialysate output of the dialyzer;

(d) a blood pump for circulating blood through an extracorporeal blood circuit, the blood circuit including the blood compartment, the blood input, and the blood output of the dialyzer;

(e) a flow equalizer comprising a first chamber and a second chamber substantially equal in volume to the first chamber, each chamber being divided into a pre-dialyzer compartment and a post-dialyzer compartment, the pre-dialyzer compartment of the first chamber and the post-dialyzer compartment of the second chamber being operable to alternately fill and empty simultaneously, and the post-dialyzer compartment of the first chamber and the pre-dialyzer compartment of the second chamber being operable to alternately fill and empty simultaneously alternately with the pre-dialyzer compartment of the first chamber and the post-dialyzer compartment of the second chamber;

(f) a closed hydraulic loop in the dialysate circuit between the first and second chambers, the closed loop including the dialysate compartment, dialysate input, and dialysate output of the dialyzer;

(g) a UF flow meter situated in the closed loop, the UF flow meter being operable to remove a preselected amount of liquid from the closed loop; and

(h) a pressure monitor including pressure alarm limits, the pressure monitor being operable to monitor hydraulic pressure in the closed loop against the pressure alarm limits and to perform a test of the UF flow meter, in which test the UF flow meter removes a preset volume of liquid from the closed loop and the pressure monitor monitors a corresponding drop in pressure in the closed loop for a preset amount of time against the pressure alarm limits.

13. A kidney dialysis machine, comprising:

(a) a dialyzer having a dialysate compartment, a blood compartment separated from the dialysate compartment by a dialysis membrane, a dialysate input, a dialysate output, a blood input, and a blood output;

(b) a source of liquid dialysate;

(c) a dialysate supply pump for circulating the dialysate from the dialysate source through a dialysate circuit, the dialysate circuit including the dialysate compartment, the dialysate input, and the dialysate output of the dialyzer;

(d) a blood pump for circulating blood through an extracorporeal blood circuit, the blood circuit including the blood compartment, the blood input, and the blood output of the dialyzer;

(e) a flow equalizer comprising a first chamber and a second chamber substantially equal in volume to the first chamber, each chamber being divided into a pre-dialyzer compartment and a post-dialyzer compartment, the pre-dialyzer compartment of the first chamber and the post-dialyzer compartment of the second chamber being operable to alternately fill and empty simultaneously, and the post-dialyzer compartment of the first chamber and the pre-dialyzer compartment of the second chamber being operable to alternately fill and empty simultaneously alternately with the pre-dialyzer compartment of the first chamber and the post-dialyzer compartment of the second chamber;

(f) a first pressure equalizer coupled to the inlet of the flow equalizer for equilibrating hydraulic pressures at the inlets of the pre-dialyzer and post-dialyzer compartments; and

(g) a second pressure equalizer coupled to the outlet of the flow equalizer for equilibrating hydraulic pressures at the outlets of the pre-dialyzer and post-dialyzer compartments.

14. A kidney dialysis machine, comprising:

(a) a dialyzer having a dialysate compartment, a blood compartment separated from the dialysate compartment by a dialysis membrane, a dialysate input, a dialysate output, a blood input, and a blood output;

(b) a source of liquid dialysate;

(c) a dialysate supply pump for circulating the dialysate at a dialysate flow rate from the dialysate source through a dialysate circuit, the dialysate circuit including the dialysate compartment, the dialysate input, and the dialysate output of the dialyzer;

(d) a blood pump for circulating blood through an extracorporeal blood circuit, the blood circuit including the blood compartment, the blood input, and the blood output of the dialyzer;

(e) a flow equalizer comprising a first chamber and a second chamber substantially equal in volume to the first chamber, each chamber being divided into a pre-dialyzer compartment and a post-dialyzer compartment, the pre-dialyzer compartment of the first chamber and the post-dialyzer compartment of the second chamber being operable to alternately fill and empty simultaneously, and the post-dialyzer compartment of the first chamber and the pre-dialyzer compartment of the second chamber being operable to alternately fill and empty simultaneously alternately with the pre-dialyzer compartment of the first chamber and the post-dialyzer compartment of the second chamber;

(f) a sensor for determining end-of-stroke times for the first and second chambers of the flow-equalizer, the sensor being hydraulically coupled to the flow-equalizer outlet; and

(g) a pump, responsive to the sensor, operable to increase the dialysate flow rate if the sensor detects an excessive end-of-stroke time.

15. A kidney dialysis machine, comprising:

(a) a dialyzer having a dialysate compartment, a blood compartment separated from the dialysate compartment by a dialysis membrane, a dialysate input, a dialysate output, a blood input, and a blood output;

(b) a source of liquid dialysate;

(c) a dialysate supply pump for circulating the dialysate from the dialysate source through a dialysate circuit, the dialysate circuit including the dialysate compartment, the dialysate input, and the dialysate output of the dialyzer;

(d) a blood pump for circulating blood through an extracorporeal blood circuit, the blood circuit including the blood compartment, the blood input, and the blood output of the dialyzer; and

(e) a flow equalizer comprising a first chamber and a second chamber substantially equal in volume to the first chamber, each chamber being divided into a pre-dialyzer compartment and a post-dialyzer compartment, the pre-dialyzer compartment of the first chamber and the post-dialyzer compartment of the second chamber being operable to alternately fill and empty simultaneously, and the post-dialyzer compartment of the first chamber and the pre-dialyzer compartment of the second chamber being operable to alternately fill and empty simultaneously alternately with the pre-dialyzer compartment of the first chamber and the post-dialyzer compartment of the second chamber, each pre-dialyzer compartment having an inlet and an outlet and each post-dialyzer compartment having an inlet and an outlet, the flow equalizer further comprising inlet valves each having an outlet hydraulically coupled to the inlet of the corresponding pre-dialyzer and post-dialyzer compartment, and outlet valves each having an inlet hydraulically coupled to the outlet of the corresponding pre-dialyzer and post-dialyzer compartment, wherein the inlets of the valves coupled to the inlets of the pre-dialyzer compartments are hydraulically coupled together and the inlets of the valves coupled to the inlets of the post-dialyzer compartments are hydraulically coupled together so as to form a flow-equalizer inlet, and wherein the outlets of the valves coupled to the outlets of the pre-dialyzer compartments are hydraulically coupled together and the outlets of the valves coupled to the outlets of the post-dialyzer compartments are hydraulically coupled together so as to form a flow-equalizer outlet.

16. A kidney dialysis machine, comprising:

(a) a dialyzer having a dialysate compartment, a blood compartment separated from the dialysate compartment by a dialysis membrane, a dialysate input, a dialysate output, a blood input, and a blood output;

(b) a source of liquid dialysate;

(c) a dialysate supply pump for circulating the dialysate from the dialysate source through a dialysate circuit, the dialysate circuit including the dialysate compartment, the dialysate input, and the dialysate Output of the dialyzer;

(d) a blood pump for circulating blood through an extracorporeal blood circuit, the blood circuit including the blood compartment, the blood input, and the blood output of the dialyzer;

(e) a flow equalizer comprising a first chamber and a second chamber substantially equal in volume to the first chamber, each chamber being divided into a pre-dialyzer compartment and a post-dialyzer compartment, the pre-dialyzer compartment of the first chamber and the post-dialyzer compartment of the second chamber being operable to alternately fill and empty simultaneously, and the post-dialyzer compartment of the first chamber and the pre-dialyzer compartment of the second chamber being operable to alternately fill and empty simultaneously alternately with the pre-dialyzer compartment of the first chamber and the post-dialyzer compartment of the second chamber, each pre-dialyzer compartment having an inlet and an outlet and each post-dialyzer compartment having an inlet and an outlet, the flow equalizer further comprising inlet valves each having an outlet hydraulically coupled to the inlet of the corresponding pre-dialyzer and post-dialyzer compartment, and outlet valves each having an inlet hydraulically coupled to the outlet of the corresponding pre-dialyzer and post-dialyzer compartment, wherein the inlets of the valves coupled to the inlets of the pre-dialyzer compartments are hydraulically coupled together and the inlets of the valves coupled to the inlets of the post-dialyzer compartments are hydraulically coupled together so as to form a flow-equalizer inlet, and wherein the outlets of the valves coupled to the outlets of the pre-dialyzer compartments are hydraulically coupled together and the outlets of the valves coupled to the outlets of the post-dialyzer compartments are hydraulically coupled together so as to form a flow-equalizer outlet;

(f) a first pressure equalizer coupled to the inlet of the flow equalizer for equilibrating hydraulic pressures at the inlets of the pre-dialyzer and post-dialyzer compartments; and

(g) a second pressure equalizer coupled to the outlet of the flow equalizer for equilibrating hydraulic pressures at the outlets of the pre-dialyzer and post-dialyzer compartments.